Subject: Chain drive
From: ACRE
Date: 10/22/2003, 6:35 AM



Here is another drawback to a chain drive.
If you lower the engine so the chain drive thrust line to come out in
the right place you lose a lot of valuable volume in the
cowl for  the cooling system. In the planetary case you
have room under the engine for the water rad.

What is shown here is a four inch lower pulley and a 12 inch upper
pulley for a 3:1 reduction ratio necessary to get the
most amount of power out of an RX8 engine.

Paul Lamar



-HarrisonYoung wrote:


This is the most convincing argument against a chain drive I've heard.
I hadn't thought about this problem. My particular interest
is a rotary installation in a twin-engine plane. It's possible
that the drives could be offset to the side instead of top or bottom,
but that would result in some rather bizarre motor mount requirements.
You've finally convinced me to stick to planetary gears :)

Harrison Young


Harrison,

Here are some more pictures and illustrations for the light weight
hollow prop shaft that nobody has tried yet. The idea here is to
use the pinion shafts to connect the prop shaft directly to the
rotating planet carrier. This minimize the load path and eliminates
the cost and weight of splines. The same idea is used on the prop
end. The prop drive lugs are welded directly to the flared hollow prop
shaft. These are threaded internally for the prop clamping bolts.
No conventional prop shaft steel flange is used. This in theory cuts
the weight greatly. The prop flange (spacer, back up washer) shown
can be light weight aluminum as there is no load on it.

Since you have an NC mill and you are willing to build your own PSRU
you are the ideal person to try this idea.

I'll send some pictures of the planet gear set shortly so you can get
a feel for how small and light weight it really is.

Paul Lamar



More pictures and illustrations. The full color illustration was done by Butch.
The airplane is Ed Anderson's rotary powered RV6 and the picture was taken from
Tracy's porch at Shady Bend Air park in Florida. If I can hold this at arms length
you know it does not weigh much :)

BTW several 3 rotor turbo airplanes have flown with the four pinion versions
so we know it is hell for leather stout. The six pinion version shown here
has 50% more torque capacity.

Paul Lamar


"Burns, Mark" wrote:


Paul;

        This PSRU fits inside the bell housing shown in the drawing. If that
is the case I wonder if that isn't what Mid West engines is doing. Check
out the engine installed on the airplane in this picture.
www.avnet.co.uk/midwestengines/htm/hawk_0.html Notice the bell
housing on the front of the engine.

Thanks,
Mark



I am pretty sure Midwest is using a simple spur gear psru with a large rubber
coupling. As I recall they use the same rubber coupling a lot of small early
race cars used as U-joints in the rear independent suspension.

IMHO they would be better off with a planetary and a Tracy style rubber coupling.

In one of these pictures you can see the channels used for air cooling the
rotors. IMHO they would be better off with oil cooled rotors like the Mazda.

Paul Lamar


"Burns, Mark" wrote:


Paul;

        I had an idea concerning your hollow prop shaft PSRU. The idea of welding
 pinion shafts onto the hollow prop shaft has always bothered me. In fact, 
I know of aircraft manufacturers that would never allow a part with the 
kinds of stresses on a prop shaft to be held together with a weld. Still 
yet I liked the idea. I think I found a solution that would not only 
eliminate the weld but also make it much simpler to mass-produce. 
Unfortunately it would make it heavier, but not that much. Instead of
 welding pinion shafts to the prop shaft simply thicken the walls, then 
drill out and tap holes in the end of the thicker walls in the ends and 
use bolts to hold the planet gears on one end and the prop flange and 
prop on the other. I think this would increase the reliability, cause 
fewer problems with the prop shaft becoming imbalanced, and mass production 
much simpler. It would be slightly heavier due to the increased metal 
in between where the pinion shafts were on your original design. 
This way it could be made very easily with a lathe, drill press, 
and tap, and eliminate welding.
        Just an idea, Tell me what you think.

Thanks,
Mark


After Shady Bend Mark.

Paul Lamar
 
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